Hitherto, various piezoelectric oscillator parts have been proposed as oscillators or filters. A piezoelectric oscillator part, in which a piezoelectric oscillator oscillates, requires a packaging structure which does not hinder the oscillation of the piezoelectric oscillator. The piezoelectric oscillator part disclosed in Patent document 1 employs a packaging structure constituted by a case substrate and a cap.
FIGS. 8(a) and 8(b) are exploded perspective views of a conventional piezoelectric oscillator part having such a packaging structure. A piezoelectric oscillator part 101 includes a piezoelectric oscillator 103 mounted on a case substrate 102. Here, first and second terminal electrodes 104 and 105 for external electrical connection are formed in the first and second corner portions 102a and 102b of the case substrate 102. Conductive adhesive portions 106 and 107 are arranged on the surface of the case substrate 102. The conductive adhesive portions 106 and 107 are electrically connected to wiring electrodes 108 and 109. The piezoelectric oscillator 103 is fixed to the case substrate 102 with the conductive adhesive portions 106 and 107, and the piezoelectric oscillator 103 is electrically connected to the first and second terminal electrodes 104 and 105 via the wiring electrodes 108 and 109. The piezoelectric oscillator 103 is supported by the conductive adhesive portions 106 and 107 at one end thereof using a cantilever structure.
To form a space for preventing the oscillation of the above-described piezoelectric oscillator 103 from being hindered, a cap 110 having an opening therebelow is connected to the case substrate 102 with a frame-shaped adhesive layer 111 therebetween.
Hence, the piezoelectric oscillator 103 is sealed in a package formed by the case substrate 102 and the cap 110.    [Patent Document 1]: Japanese Unexamined Patent Application Publication No. 2001-110925.
Also in the piezoelectric oscillator part 101, similarly to other electronic parts, reduction in size is strongly required. However, in the piezoelectric oscillator part 101, a packaging structure having a sealed space, as described above, needs to be formed in order not to hinder the oscillation of the piezoelectric oscillator 103. Hence, reduction in the size of the piezoelectric oscillator part 101 has been limited.
Hence, to reduce the size of the piezoelectric oscillator part 101 as much as possible, in the case substrate 102, the distance between the conductive adhesive portion 106 and the first terminal electrodes 104, and the distance between the conductive adhesive portion 107 and the second terminal electrode 105 have conventionally been made as small as possible.
On the other hand, in the piezoelectric oscillator part 101, the oscillation of the piezoelectric oscillator 103 is apt to leak to the case substrate 102 side through the junctions formed by the conductive adhesive portions 106 and 107. This leakage of oscillation may cause deterioration in resonance characteristics and the like.